128 Analysis and Valuation of Manures [203 



into a tall beaker, diluting to about 50 c.c. Add good excess 

 of bromine and boil to oxidise the carbonaceous matter. 

 When the bromine has all gone, make just alkaline with am- 

 monia. Add about 5 grams of pure ammonium acetate, then 

 make just acid with acetic acid. Bring the liquid up to a boil, 

 then cool quickly, and filter. Wash with hot water containing a 

 little ammonium nitrate. This precipitate contains the normal 

 phosphates of iron and aluminium. (Some analysts weigh this 

 precipitate, and consider the Fe 2 3 and A1 2 3 to constitute 

 half its weight. This, however, leads to faulty results.) Dis- 

 solve the precipitate in dilute nitric acid, collecting the liquid 

 in a 4-oz. conical flask fitted with an india-rubber stopper. Add 

 about 5 c.c. of strong NH 4 N0 3 solution j heat nearly to boiling 

 (85 C. is the correct temperature). Add 25 c.c. of ammonium 

 molybdate solution. Cork up the flask, and shake vigorously 

 for about three minutes. Filter off the yellow precipitate, 

 which will contain all the phosphoric acid. Make the filtrate 

 alkaline with ammonia, boil, and filter. The precipitate will 

 consist of the hydrates of iron and alumina, slightly contami- 

 nated with molybdic acid. To remove this, dissolve in HC1 

 and reprecipitate with ammonia. Wash well, dry, ignite, and 

 weigh as Fe 2 3 + Al 2 3 . To separate these two, dissolve 

 in strong HO. 1 Make up to 250 c.c. with water. Mix the 

 solution thoroughly, and determine the iron as described in 

 paragraphs 75-77- 



203. Calculation of Results.— Phosphoric acid. This 

 is calculated as P 2 5 from the Mg 2 P 2 7 . It is always best in 

 calculating results to begin by finding the percentage which the 

 precipitate is of the substance taken. Thus we should begin 

 by multiplying the weight of Mg 2 P 2 7 by 100, and dividing it 

 by the weight of mineral phosphate which has been used. 



1 It will often be found that this precipitate, after ignition, is very 

 insoluble in HC1. Some analysts always use H 2 S0 4 , which acts more 

 rapidly. 



